The clinical laboratory has available to it a variety of instruments for conducting or performing these measurements. The difficulty in the prior art has been the challenge of supplying a reference or control material to compare the output of the instrument with that obtained on a sample of known constituency. For example, in the common blood analysis test that is performed, it is necessary to supply a standard sample having a known amount of the particular material that is being determined. Often, this standard is provided in various composition forms so that the results obtained on the instrument can be verified and correlated over a range of values.
In dealing with solid or dissolved materials such as protein, cholesterol, blood urea, enzymes and the like, it is usually a straightforward matter to supply as part of the reference solution a known amount of the particular material being determined. When one is seeking to determine pH, pO.sub.2 and pCO.sub.2 however, the situation is somewhat more complicated. The instrument itself is more complex because the nature of gas measurement requires the use of special electrodes and membranes. Any blood gas control, to be suitable, must be compatible with the electrodes and membranes. Since gases are involved, gas controls themselves cause problems because of the difficulty in supplying a liquid in which the known amounts of oxygen, carbon dioxide and the known value of pH are stable over significant periods of time. Various controls have been available and some of these are referred to later in the section on Prior Art. As used herein the terms "control", "reference solution" and "standard" are used to include fluids which may be used to verify values obtained from a blood gas-determining instrument on an unknown sample or which can be used as the calibrating material for that instrument. For example, in the usual situation, a sample of blood is introduced into the appropriate laboratory instrument and a value for a parameter, pO.sub.2, for example, obtained. The technician does not know whether that value is correct for the sample introduced. If he introduces into the instrument a control material having a known value for pO.sub.2, he can then compare the instrument read-out with the known value and determine whether or not the instrument is performing properly. On the other hand, that same control material can often be used as a calibrating fluid whereby the technician simply adjusts the reading obtained on the instrument to coincide with the known value of the control.